Lubricating oil



Patented Jan. 14, 1 947 LUBRICATING 01L Elliott Alfred Evans and John Scotchford Elliott,

Beaconsfield, England, assignors to C. C. Wakefield & Company Limited, Beaconsfield, England, a British company No Drawing. Application August 24, 1943, Serial N0. 499,350. In Great Britain July 29, 1942 This invention consists of improvements in or relating to lubricating oils and the general object is to produce lubricating oils containing minor proportions of addition agents which improve the qualities of the lubricating oils under various con ditions (such for example as conditions of extreme pressure) and which also-prevent undesirable attack on metal surfaces such as bearing surfaces.

Addition agents previously proposed for use with lubricating oils (including mineral oils) include organic polysulphides having a carboxyl or ester substituent, sulphured fatty bases, mixtures of halogenated organic compounds and sulphur compounds, thioethers (with or Without compounds containing active sulphur or halogens or both), and organic compounds containing at least two halogen atoms and at least one nitro group in the molecule.

The majority of extreme pressure lubricants and cutting lubricant contain either sulphur (which may be present as elementary sulphur or as sulphur chemically combined in a number of Ways e. g. as sulphured fatty oils or acids or as organic polysulphides) or halogens which may also be introduced in a variety of derivatives, or both.

Some of these compositions are liabl under certain conditions to cause corrosion of metal surfaces with which they come into contact. Thus it is well known, for example, that free sulphur produces at elevated temperatures a black stain 01 copper sulphide on metallic copper, whereas halogenated compounds are particularly liable to pro duce corrosion on steel and other ferrous alloys By the selection of suitable halogen compounds in which the halogen is moderately firmly attached to the molecule of which it forms a part, this corrosion of ferrous alloys can be to a large extent prevented.

On the other hand, it is often desirable to employ lubricants containing active sulphur, especially for cutting purposes or in hypoid gears where very high pressures are encountered, so that the elimination or reduction of undesirable corrosion of copper and cuprous alloys is a matter of considerable importance. Moreover the corrosion produced by active sulphur i often increased by the additional presence of halogenated compounds.

It is the specific object of this invention to provide protection against such corrosion of copper or cuprous alloys by lubricating oils containing active sulphur with or without additional halogen compounds.

3 Claims. (01. 25347.5)

The term active sulphur is employed to designate sulphur which will react with metallic copper,

It ha now been found that when a lubricating oil-has additons of the types above referred to which might giveasulphur attack to metal surfaces, protection against such attacks may be provided by the further addition of a compound of the group consisting of a mercapto-arylenethiazole, or a derivative thereof such as an arylthiazyl-di-sulphide or an aryl-thiazyl-hyd'roxyalkyl sulphide, or an alkyl thiuram monoor disulphide. Examples of suitable further additions are mercap-tobenzo-thiazole, benzothiazole disulphide or benzothiazole-hydroxy-methyl ulphide (which is produced by the action of formaldehyde on mercaptobenzothiazole), or tetramethyl or tetraethyl thiuram disulphide.

According to this invention a lubricant (particularly a lubricant containing hydrocarbon oil) has dispersed therein a minor proportion of an addition agent containing active sulphur such as an organic polysulphide or a sulphured fatty oil with or without a halogenated organic compound, such as a chlorinated parafiin wax or nitro-p'olychloro benzene and also a minor proportion of a mercapto-arylene-thiazole or a derivative thereof, or an alkyl thiuram monoor di-sulphide.

In a preferred form a lubricant according to this invention has dispersed therein a minor proportion of an organic polysulphide comprisin a carboxyl or ester substituent such as a disulphide, trisulphide or tetrasulphide derived from an arcmatic hydroxy ester or mixtures thereof and also a minor proportion of a mercapto compound as referred to in the preceding paragraph. A preferred compound is 2-mercapto-benzothiazole.

The nature of this invention and of subsidiary features thereof will be appreciated from the following examples:

Ezrample 1 An extreme pressure lubricant was prepared by dissolving one part of a mixture of di(3-carbo methoxyl-hydroxyphenyl) polysulphide (containing 13 per cent of active sulphur) and eight parts of a chlorinated parafiin wax (containing about 40% chlorine) in'9l parts of a mineral lubricating oil.

Small pieces of polished pure copper foil were placed in beakers containing grams of this oil and heated (a) at 100 C. for 1 hour, (b) at 100 C. for 16 hours, (0) at C. for 1 hour.

At the conclusion of these tests the appearances of the copper test pieces showed tarnishing 3 which in certain circumstances would be unwanted.

To another sample of this oil was added 0.1 per cent of 2-mercaptobenzothiazole, and parallel tests were carried out. At the conclusion of these tests the copper test pieces shewed definitely less tarnishing or practically none.

Example 2 Ten grams of a sulphured cutting oil were placed in a petridish and heated with a piece of pure polished copper foil for -16 hours at 100 0.

The copper was badly blackened and large flakes of copper sulphide couldbe wiped off.

To the same oil was added 0.1 per cent of benzothiazole disulphide, and the test repeated.

The copper was uniformly'tarnished but perfectly smooth and free from particles of copper sulphide.

Parallel tests carried out with other sulphur compounds e. g. p-thiocresol, dibenzyl disulphide and di(3-carbomethoxy-4-hydroxyphenyl) thioether shewed that this property was limited to the compounds of this invention, although in the caseof the last compound a limited degree of protection appeared to be afiorded.

The amounts of these compounds which are to be employed will depend on several factors:

(I) The amount of active sulphur present in the oil to be inhibited.

(II) The condition of this "active sulphur, i. e. whether it is present as elementary sulphur, or loosely combined asin the case of many organic polysulphides; 1

(III) The presence of additional halogen compounds and their nature. Thus an oil containing 0.5 per cent of a mixture of di(3-carbomethoxyl-hydroxyphenyl) polysulphides (containing 13 per cent of active sulphur), was completely inhibited against copper staining at 100 0., by

the addition of as little as 0.02 per cent of 2-mercaptobenzothiazole.

In other cases, such as sulphurized oils containing much elementary sulphur, it may be desirable to use as much as 0.3 per cent, or even more of the inhibitor.

It is inadvisable to use more inhibitor than is necessary to reduce the staining to the desired degree, as the E. P. properties of the oil may thereby be impaired.

We claim:

1. An extreme pressur lubricant comprising a major proportion of a hydrocarbon mineral oil, anextreme pressure addition agent consisting of a di(3-carbomethoxy-4-hydroxyphenyl) polysulphide and an organic corrosion inhibitor selected from the group consisting of Z-mercaptobenzothiazole and benzothiazole disulphide present in amount less than 0.5 per cent and sufiicient to eliminate corrosion of copper and cuprous alloys but insufficient materially to enhance the extreme pressure properties of the composition;

2. An extreme pressure lubricant comprising a major proportion of a hydrocarbon mineral oil, an extreme pressure addition agent consisting of a di(3-carbomethoxyl-hydroxyphenyl1 polysulphide, a chlorinated paraffin wax and an or, ganic corrosion inhibitor selected from the group consisting of Z-mercaptobenzothiazole and benzothiazole disulphide present in amount less than 0.5 per cent and sufiicient to eliminate corrosion of copper and cuprous alloys but insufficient materially to enhance the extreme pressure properties of the composition. 1 1

3. A lubricant according to claim 1 wherein the polysulphide is present in amounts between 0.5 and 2.0 per cent and the organic corrosion inhibitor in amounts not exceeding 0.3 per cent.

ELLIOTT ALFRED EVANS. JOHN SCO-TCHFORD ELLIOTT. 

